Asymmetric distortion of alkane radical cations as studied by EPR spectroscopy: The role of pseudo-Jahn-Teller effects and matrix interactions

Abstract

In a series of recent works we have shown that the radical cations of several alkanes, such as propane, norbornane, n-pentane, and its methyl-substituted derivatives, which do not have degenerate HOMOs, are distorted in several matrices at low temperatures. These cations distort in a direction unique to each system regardless of the matrix employed, but the extent of deformation is dependent on the matrix. The two equivalent distorted structures are dynamically averaged at elevated temperatures. From these observations, the mechanism of the distortion was attributed to a pseudo-Jahn-Teller (JT) effect assisted by matrix interactions. The distortion of ethylene cation recently observed by EPR spectroscopy is rationalised in the same way. This paper is a review of our studies of the title phenomenon. © Acta Chemica Scandinavica 1997.